Humphreys et al.: Identification of Pseudopentaceros wheelen recruits 



457 



Somerton and Kikkawa, 1992). Owing to sustained low 

 annual catches at the Hancock Seamounts, the Na- 

 tional Marine Fisheries Service (NMFS) Honolulu Labo- 

 ratory implemented both a research stock assessment 

 program in 1985 and recommended institution of a 

 moratorium (in effect since 1986) prohibiting trawl 

 fishing at the Hancock Seamounts (Somerton and 

 Kikkawa, 1992). The remainder of the SE-NHR sea- 

 mounts, which represent some 90% of the historical 

 trawl fishery in terms of habitat and overall catch, lie 

 in international waters and under no fishery manage- 

 ment control. As increases in armorhead biomass at 

 Hancock and other SE-NHR seamounts appear to de- 

 pend exclusively on recruitment, recent work has fo- 

 cused on examining the temporal pattern of seamount 

 recruitment and the biological characteristics of new 

 recruits. Boehlert and Sasaki (1988) used monthly 

 length-weight data recorded by the Japanese at four 

 SE-NHR seamounts during May 1972-December 1973 

 to estimate the seasonality of recruitment. Assuming 

 that new recruits have a condition factor of >2.0, they 

 found recruitment highest during April-May 1973 and 

 secondary peaks in August 1972 and July 1973. An- 

 nual recruitment to Southeast (SE) Hancock Seamount, 

 one of two guyots composing the Hancock Seamounts, 

 was sporadic between 1978 to 1990. Strong recruit- 

 ment (>50% of population biomass) at SE Hancock Sea- 

 mount occurred only in 1980 and 1986, and moderate 

 recruitment (ca. 20-30% of population biomass) in 1988 

 and 1990, based on catch per unit of effort (CPUE) 

 and FI distributions derived from Japanese trawl data 

 and NMFS stock assessment surveys (Somerton and 

 Kikkawa, 1992). 



Little further progress, however, has been made in 

 discerning the timing of recruitment and biological 

 characteristics of newly arrived recruits. The apparent 

 temporal variability in recruitment, the change in FI 

 during time elapsed between recruitment and sam- 

 pling, coupled with limited sampling opportunities, 

 make the identification and study of new recruits and 

 their temporal recruitment pattern problematic. A po- 

 tential alternative for identifying newly recruited 

 armorhead uses biological indicators to distinguish a 

 new seamount arrival from longer resident armorhead. 

 Parasites have been frequently used as biological indi- 

 cators in fish and their benefit to studies of fish stock 

 separation, movement, and diet are numerous (Wil- 

 liams et al., 1992). In relation to seamount studies, 

 differences in the trematode parasite fauna of sable- 

 fish off Canada's west coast led Kabata et al. (1988) to 

 surmise that seamount populations of sablefish are 

 distinct and separate from those sablefish inhabiting 

 the continental slope. Since seamount armorhead popu- 

 lations are derived from epipelagic individuals, we ex- 



amined specimens of both life history phases for para- 

 site differences and other distinguishing features. We 

 report on the feasibility of using a monogenean gill 

 parasite and two condition indices as potential indica- 

 tors of new seamount recruits. 



Methods 



Epipelagic specimens of P. wheeleri (n = 53) were inci- 

 dentally captured from the central North Pacific 

 (around lat. 45°N, long. 155°W) in July 1984 and 1985 

 and from the eastern North Pacific (around lat. 46°N, 

 long. 129°W) in July 1985 by the Japanese fishing 

 vessels Oshoro Maru and Tomi Maru No. 88, respec- 

 tively, during salmon longline and surface drift gill- 

 net operations. These specimens were saved intact and 

 stored frozen prior to examination. Specimens of sea- 

 mount armorhead (n = 1,220) were collected from the 

 southern end of the SE-NHR at SE Hancock Seamount 

 (29°48'N, 179°04'E; see Fig. 1) by bottom longline gear 

 during research cruises of the NOAA ship Townsend 

 Cromwell in June 1985, August and October 1986, April 

 and August 1987, and January, July, August, and No- 

 vember 1988. All seamount specimens were derived 

 from efforts beginning in 1985 to estimate armorhead 

 relative abundance (catch per unit of effort) at SE 

 Hancock Seamount by using standardized assessment 

 techniques described in Somerton and Kikkawa (1992). 

 Seamount specimens were either saved intact and 

 stored frozen, or gills and viscera were removed and 

 preserved at sea in either alcohol-formalin-acetic acid 

 (AFA) solution or placed in a dilute (0.0004%) formalin 

 solution for several hours and then preserved in 10% 

 formalin. Collection data for armorhead specimens in- 

 cluded body weight, FL, body depth at first anal spine, 

 sex, and date and location of capture. Measurements 

 were made to the nearest millimeter, and body weight 

 to nearest gram. 



Under a dissecting microscope, the gill arches and 

 visceral organs of armorhead specimens were exam- 

 ined for macroparasites. Guidelines proposed by 

 Sindermann (1983) were followed to determine which 

 species have potential as biological tags. Ideal para- 

 site characteristics include ease of detection and iden- 

 tification, a single host-life cycle, and temporal stabil- 

 ity in prevalence. Furthermore, the parasite should 

 persist in the host during the study, and prevalence 

 should differ significantly between study areas. These 

 criteria were best fulfilled by the monogenean 

 Microcotyle macropharynx (Mamaev), based on exami- 

 nations of the seven parasite taxa (monogenean 

 Trochopus sp., digenean Bivesicula sp., larvae of the 

 nematode Anisakis type I, nematode Hysterothylacium 



